1. Field of the Invention
The invention relates to electronic navigation systems, and more particularly to a method and apparatus for providing navigation route guidance information in audible and/or visible form. The guidance information is provided to the operator of a land vehicle along a desired route between a start location and a desired destination as specified by the operator.
2. Description of the Prior Art
A variety of different navigation devices have been developed for providing the operator or user of a land vehicle with adequate guidance information along a route of travel. For example, one prior art device performs a route search to a target destination, attaining visible and/or audible guidance of a route to the destination by the use of maps. Another prior art device displays only a map covering a certain range with the vehicle's present position as its center point.
Conventional navigation systems with route search and guidance functions may include systems for performing concise and simple guidance by displaying a limited amount of information such as the distance to a next-to-turn road intersection during travel and guidance along a presently recommended route.
Another system is disclosed, for example, in Published Unexamined Japanese Patent Application (PUJPA) No. 4-335390. This system is capable of simultaneously providing the positional relationship of a destination and the present position of the vehicle and its surroundings by making use of dual screens which permit visual indication of a wide-area map covering both the present location and the destination along with a precise or detailed map around the present position.
A further prior art navigation system is capable of providing simple information concerning the direction of travel by displaying travel images using three-dimensional (3D) visual effects. Unfortunately, this system is designed to limit necessary guidance information to a minimum and results in a "trade-off", as discussed below. While this system may offer certain advantages, such as an increase in the visibility of guidance information displayed, the system suffers from a problem in that information tends to become insufficient in some cases.
With the system designed to display a wide-area map and detailed map using two divided screens, the vehicle operator may recognize the positional relationship of the destination and the present vehicle location in addition to the detailed information near or around the present location. However, the display of detailed information near the present vehicle location decreases by half in the display region due to employment of the two-screen division scheme. Another problem faced with this system is that recognizability of detailed on-map information displayed decreases with a reduction in the display scale (to enlarge a displayable coverage on the screen).
With the system using a 3D-display scheme for display of travel images, there is a drawback that a sufficient amount of information will not be available on the maps.